Thermal time lag fuse



Jan. 26, 1954 A.' BERTHEL THERMAL TIME LAG FUSE Filed May s, 1948 3 Sheets-Sheet l .d i e a? M k 2 i7 uin-El Jan. 26, 1954 G. A. BERTHEL THERMAL TIME LAG FUSE 3 Sheets-Sheet 2 Filed May 8, 1948 Z i W 3 4 n & n m g a Jan. 26, 1954 e. A. BERTHEL THERMAL TIME LAG FUSE 3 Sheets-Sheet 5 Filed May 8, 1948 Patented Jan. 26, 1954 THERMAL TIME LAG FUSE Gust A. Berthel, Chicago, 111., assignor to Jefferson Electric Company, Bellwood, 111., a corporation of Illinois Application May 8, 1948, Serial No. 25,831

This invention relates to an improved thermal time lag fuse in which the circuit breaking action may be provided by thermal responsive means other than the usual fuse link, and the invention relates also to a fuse link which is especially adapted for use in a cartridge fuse.

It is an object of my invention to provide a fuse link having thermal time lag means integrally incorporated therewith.

Fuses especially of the cartridge type, are frequently provided with means which serve to delay opening of the fusible element or link under low or moderate overload conditions. This type of fuse is oftentimes referred to as a time lag fuse. By the term "thermal time lag fuse, I referv to a time lag fuse which includes a body of fusible material which serves as a connecting link between two elements, at least one of which is stressed. The arrangement of'parts is such that as the body of fusible material becomes softened, due to the increased temperature developed by small or moderate overload conditions, the stressed part is released, thus serving to open the circuit through the fuse.

A further object of my invention is to provide a thermal time lag fuse which is extremely simple in construction, and economical. to manufacture, and which occupies substantiallyno more room than an ordinary fuse. Thus the fuse embodylng my invention con be used in the usual type of cartridge fuse.

Another object of my invention is to provide a thermal time lag fuse construction having a resilient member in the form of a leaf spring.

The leaf spring not only requires less space than a coil spring, but since it has a larger cross sec- .tion, it can be used as one of the current carry- .ing parts.

design is provided in order to obtain the blowing characteristics desired.

Still another object of my'invention is to pro- -vicle a fuse the maximum operating temperature of which is less than 300 degrees F.; thus, cooler operation and a lower watt loss is provided.

A further object of my invention is to provide 18 Claims. (Cl. 200-123) in a thermal time lag fuse construction,'a resilient member which can be manufactured by a punching process, thereby providing enhanced uniformity of mechanical and electrical characteristics at low unit cost.

Other objects, features and. advantages will become apparent as the description proceeds.

With reference now to the drawings, in which like reference numerals designate like parts,

Fig. l is an elevation, partly broken away, of one embodiment of my invention;

Fig. 2 is an end view of the embodiment shown in Fig. 1;

Fig. 3 is a plan view of just the fuse link portion of the fuse shown in Fig. 1;

Fig. 4 is an end view of the fuse link portion shown in Fig. 3

Fig. 5 is an elevation of the fuse link portion of Fig. 3, but showing the parts in a changed position;

Fig. 6 is a section taken along line 66 of Fig. 5;

Fig. 7 is an elevation, partially broken away of another embodiment of my invention;

Fig. 8 is an end view thereof;

Fig. 9 is a plan view of the fuse link portion of the Fig. 7 device;

Fig. 10 is an end view of the fuse link portion shown in Fig. 9;

Fig. 11 is an elevation of the fuse link portion shown in Fig. 9 but with the parts in changed position;

Fig. 12 is an enlarged sectional view taken along line l2-l2 of Fig. 9;

Fig. 13 is a planview, similar to Fig. 3, showing a modified form of fuse link; and

Fig. 14 is an elevation of the fuse link shown in Fig. 13..

With reference now to the embodiment shown in Figs. 1 1306, inclusive, the reference numeral 20 designates generally a ferrule type fuse, for. example, one having. a sixty ampere rating. The fuse constitutes a casing 2| having slotted end caps 22 and 23 which may be suitably crimped on the casin 2|, as by the dents 40. Within the casing are two copper strips 24 and 25, one at each end, and these are supported at their outer ends by the slotted end caps 22, 23, and at their intermediate portions by barriers M5 and 21, these barriers being in the form of disks which are stamped from a suitable insulating material, such as vulcanized fiber, of which material the casing 21 is also made.

The outer ends of the copper strips 24, 25 extend through the slots in the end caps 22, 23 and areelectrically connected therewith by solder 28. The barriers 26, 21' are also slotted, so as to receive not only the copper strips but also a bridge 29, also formed of suitable insulating material. The bridge 29 and the barriers form a. rigid structure. Lagging strips 30 and 3|, preferably of copper, are secured to the under side of the bridge 29, an eyelet 32 being used for this. purpose with respect .to the laggingstrip 30 and airivet33being used withrespect toithe lagging strip 3!.

Each of the copper strips 24, 25 has a notched or drop-out quick blowing portion 34 and an inner portion 35 which rests on the *bridge 29. The inner portion is provided-withturned.down side edges or wings 36 whichoverlap and contact the sides of the lagging strips 30, 3| in heat conducting relationship.

A leaf spring 31 formed of suitable'springmaterial which is not affected by elevated temperatures is anchored at 10116 of its ends by means of therivet .33, .the rivet holding .the .spring against copper strip 315 .in .a manner .so as to provide :an electrical contact. I The spring 1311 lis preferably made of .beryllium copper. Thecpposite or'free end of the .sprfingisprovi'ded with a...bent down end 38, and .the spring is, its normal condition, stressed so that the .en'df3'8 is received Within the eyelet 13.2 .andismaintaine'd in its stressed position" by .a body of solder .39. The solder. preferably has amelting point diapp'roximately 280 The .end, portions of the...interio.r .of the casing "2| are filled with fuse powder 4!, the barriers 2.6 and .21 serving .to confinethe fuse powder to said end portions, thereby leaving the central .portionof the interior of the casing L24 unob- "structed'to permit free operation of the spring 3'1.

in operation, theparts areso designed that underishortcircuit conditions, thefuse willlblow at'the drop-out portions'34 of either one of the copper strips. or .25. .However, .under allow roverload .condition, the. current passing through these copper strips .24 and 25, and also through the spring 31 generatesa certain amounto'fheat which will gradually raise the temperature of thebody of solder 39 'to its softening-or melting point. Thus, if the overloaded condition'is continued, the solder "39 will become so soft ,Lthat itisno longersumcient to retain the spring? .Iin'its stressed position, with the resultthat the spring will be released and occupy'the position shown in Fig. 5. .Since the spring is :the only metallic connection between the two .halvesof the fuse, the opening of the spring will cause the circuit "to be opened. The eyelet constructionpermits the melted solderto run out or the eyelet, irrespective of the'angular position of the fuse with the result/that only a comparatively .Sma'll portion of the solder is volatilized.

iThe'lagging strips 30 and 3| :serve .to absorb the heat'that is generated in the :copper strips "24 and F25, and in the spring 31, andthus'they ;may' .be dimensioned so'as to control theblowing or the l'fuse.

InFigs, '7 to 12,.inclusive, abladetype cartridge -ffuse, designated generally by the reference. nu- .meral 44,.is shown. Thisfuse comprises a casing AB-having. slotted'end capsAfi and 4.1, through which extend blades 48 and 49. .A bridge 50 within the casing provides physical connection "between -the :parts and serves to support the inner ends of the blades 48, 49. .The blades are :connectcd :to the :ends iof the bridge .50 :byz-yokes 52 :and :53. czshown :in :Fig; .10, :the connectinnbetweemthe yoke,t'.the. bri'dgeiandzthe :blade includes a spacer 54, and a plurality of rivets 55. As shown in Fig. 9, the inner ends of the blades 48, 49 are provided with slotted portions 56 which are aligned with apertures 51 in the yoke 52 or 53, and with apertures in the caps 46, 41, to the end that after the parts are assembled, drive screws 58 may be driven through the .cap and .the casing-toisecure thegyokes in position. Other .drive screws 58 are zprovided for additionally securing the cap to the casing. Slotted barriers 60 and GI are carried by the bridge 50. Lagging strips 62 and 53 are secured =tothe *"upper surface of the bridge by rivets 64, their outer vends abutting against the barriers andaervingto maintain the spacing thereof.

Copper tstrips 6 and 61 extend between the ,yokes 52...and 53 and the lagging strips 62 and 633respectively. The outer ends of the copper stripsifljfil are gripped between the spacer 54 and the blade, as shown in Fig. 10, and the inner ,portions pass -through. a .slot .in the barrier 60 .crI'TS l. and .overlie. .theflagging strips and .areqsolfdered' thereto, as will" hereinafter'.bepointed out. L'Iheportions .:of the .copper strips. 366, .6] which .are. disposed between the yokes. and the barriers are notched to providedrop out,portions 6.8.

.In this embodiment of my .invention, two springs J0 and H are provided. These two springs are disposed in side by siderelationsliip. Thespring 1D isanchoredto thelagging strip 62, and lth'espring'll .is anchored-to the. lagging strip 63. The springs .are anchorediby. means of riveted extrusions 1.2 which project upwardly 'from the lagging strips .and pass through :suitable apertures in the copper strips 65 and .61, .and through other suitable apertures in'springs 10,11 I, 'respectively,..the upper ends of .thexivete'd extrusions being. headed over "as shown inFigTQ. The springs are preferably formedifromberyl- Llium .copper :and "each spring is provided with -a hingeportion 1.3, which is'in thef'form of a'half loop, and which constitutes the stressed ,portion of the spring. By this arrangement, "Lam enabled to secure lagging'strips'i'fl to the major portion of the'spring. As shown in Figfl'zlthe lagging strips "T4 and the spring itself are provided with aligned apertures .or bores 15 and .16. Molten solder 'is caused to flow 'into the 'bores'15, 1S, audit creeps outwardly away *from the bores between the contacting surfaces :0: thela'gging strips, and between the surface of the .bottom lagging strip and the top'sur'face of thespring T0. or 1 I and also between theb'ottom surface-of .th'e :spring and .the "top surface (dfithe copper strips 66 and 161. .Thus, all 'df'thegparts are maintained in electrical contacting andheat conducting relationship, and the soldered connection! between the. bottom surfaceof the spring and the upper, surface or the copper strips "56 and 61 serve to maintain the'hingeportionWB of the. sprlnglin stressed relationship. The lag- .ging strip 114 and the spring areialso securedf'to each otherby a rivet "I9, and thela'gging strips 62. and 63, are cut away, 'as indicated by"the.irference numeral 80, right beneath the rivetso as .to assure that there willbe noaarcing at 'this point.

In operation, the fuse :will blow und'er'short circuit conditions atone .or the other offlthe "drop out portions 68. However, under. low..or. moderate overload conditions, the .heatgenerated by the current .passingthrough the copper strips 6.5.and .61 will. cause "the bodiesrof esolder 11 and 418 J in each of .tthe springs 1.10 -.and v I ate he raised :in .temperature. ==As :the temperature approaches faces.

the melting point of the solder, it will become softened with the result that the bond between the under surface of the springs and the upper surface of the copper strips 66 and 61, will finally give away, causing the springs to be released as, shown in Fig. 11. The release of the two springs will be practically simultaneous, for the reason that as soon as one spring is released,

the entire electrical load will be thrown on the .erated in the copper strips, and of course the lagging strips 14 also absorb the generated heat. A further modification of the fuse shown in Figs. 3 and 5, is shown in Figs. 13 and 14. Here, the parts are substantially the same and are designated by the same reference numerals, with the exception that instead of two copper strips 24 and 25, a single copper strip 8| is provided. In addition to the drop out portions 34, a central fusing portion 82 is provided which shows a portion of the current passing through the spring 31. Thus, when the solder 39 is raised in temperature to substantially the melting point, and the spring released, an increased electrical load will be thrown on the central fusing portion 82, and this will fuse and open the circuit practically simultaneously. However, the actual opening of the circuit will take place by the fusing of the central fusing portion 82, and the characteristics of such a fusing portion are such that there is a somewhat lesser tendency toward arcing than where the circuit is broken by means of the spring 39. In this embodiment, it will be observed that the positions of the bridge 29 and of the lagging strips 30 and 3| is reversed,

in order that the central fusing portion may be spaced from the bridge.

To secure greater uniformity of operation, I have found it desirable to provide a fusible means in the form of a body of metal of substantial heat absorbing capacity. Although in the larger fuse sizes, the heat absorbing capacity of the fusible metal is comparatively small with respect to the heat absorbing capacity of the other elements of the fuse structure, the fact that the stressed portion of the fusible metal is just a part of a larger homogenous body of heat conducting and absorbing material will tend to prevent release of the resilient strip due to localized heating effects at the contacting sur- In other words, the fact that release will not occur until all of the fusible metal has been raised to the softening point provides greater uniformity of operation.

The preferred embodiments of my invention shown and described herein are illustrative only, and it is understood that various modifications and changes may be made therein without departing from the spirit of my invention as deifined in the following claims.

' I claim:

'l. A cartridge fuse comprising a substantially and providing a substantially rigid mounting therefor, said bridge being made from electrical insulating material, conducting strips extending between said terminal means and the end portions of said bridge and being provided with fusing portions, a flexurally resilient strip disposed within said casing, means anchoring one end of said resilient strip to said bridge and pro viding electrical connection with one of said conducting strips, means securing the other one of said conducting strips to another portion of said bridge, and fusible means electrically connecting said last mentioned conducting strip and the free end portion of said resilient strip and maintaining said resilient strip in flexurally stressed condition.

2. A fuse as defined in claim 1 in which the means for securing said last mentioned conducting strip to said bridge comprises an eyelet, and in which the free end of said resilient strip is provided with a bent portion adapted to be received within said eyelet, and in which said fusible means is disposed within said eyelet and surrounds said bent portion.

3. A fuse as defined in claim 2 which is provided with a body of heat absorbing material mounted on said bridge, said eyelet extending through said body of heat absorbing material whereby the temperature of said fusible means will be maintained at substantially the temperature of said body of heat absorbing material.

4. In combination with a fuse as defined in claim 14, a strip of heat absorbing material secured to said resilient strip.

5. A fuse as defined in claim 14 which is provided with a heat absorbing member mounted on said resilient strip, said heat absorbing member and said resilient strip being provided with aligned perforations and said fusible means being disposed in said aligned perforations'and contacting said last mentioned conductor means, whereby the temperature of said fusible means will be maintained at substantially the temperature of said heat absorbing member.

6. In a fuse, means providing two parallel circuits, one circuit being maintained in closed position by a comparatively small body of metal which develops a comparatively high degree of heat, and the other circuit being maintained closed by a comparatively large body of metal which is adapted to be ruptured when heated to a moderate extent, the proportions of said bodies of metal being such that under small and mod erate overload conditions said second mentioned circuit will open prior to said first mentioned circuit, thereby throwing the entire load on said first mentioned circuit, and causing the same to open, whereby only a comparatively small amount of metal is subjected to volatilization.

'7. In a fuse, two superimposed strips arranged in parallel circuit with each other, one of said strips being of limited current carrying capacity, and fusible means to maintain the other in a fiexurally stressed condition.

8. In a fuse, two superimposed strips arranged in parallel circuit with eachother, one of said strips being of limited carrying capacity, and the other of said strips being of considerably greater current carrying capacity, a body of fusible metal interlocking the end of said second strip to a portion of said first strip to maintain said second strip in a flexurally stressed condition, the arrangement being such that under moderate overload conditions said body of fusible metal will become softened to permit the release of said second strip, thereby throwing :saidaterminal-zmeans.

aeeaen the entire current load on said first mentioned strip.

"9. In combination;afuse'link, a first fusing section having a cross'section of dimensions such that "said fusing section will openunder short circuit conditions anda "second fusing section having a cross section such that it would ordinarily open prior to said first "mentioned fusing section, a resilient current carrying member shunted around said second fusing -section,- and securedat oneend to said fuse link, and a body of fusible material interlocking the otherend ofsaid resilient *member with anadjacent por tion ofsaid link to maintainsaid resilientmemher in stressed condition, whereby under small 'and"moderate'overloadconditions, said body will be-"elevated to 'a temperature such that it will permit "the release of said "resilient member, thereby-causing the full load "to be 'thrown on .saidsecond fusing section.

'10. A cartridge;'fuse"having a bridge, a fuse 'link spaced from saidbridge and-secured at either end with respect theretogand resili'ent :strip ofmetal-rigi'dly mounted at one end with "respect tosaid-fuse'link in substantially super- .imposed relationship therewith, said resilient strip being formed so that thefree end tends to spring away from saidffuse link and a body of fusiblemetal serving'to interlock the'freeendof .said resilient strip with said fuse link, whereby said resilient strip is maintained in flexurally stressed condition and in' ,parallel electric circuit with said fuse link.

$11.,In a fuse having "afltubular casing, a fuse link ,adapted'for blowing undershortcircuit conditions, and circuitopening means operative under moderate overload conditions in series circuit with said 'fuselink, said latter'means'comprising vabo'dy offusible metal and aheat ab- :sorbing member disposed .in thermally conductingrelationship with each otheran'd with said fuse link, bridgemeans for supportingxsaid' body of fusible metal, and a flexurally resilient strip securedat one end .to said bridge means-and havingits other end engaged by'saidbody of fusible ,metall and maintained-in fiexurally stressed 'con ,fdition thereby, and. means supporting said bridge :means from said casing including a disk 'dis- ,posed "between said fuse link and said circuit opening means, and engaging-said bridge means.

.12. In acartridge fusejhaving a substantially zcylindrical casing and terminal .means at the enfdspf. said casing, circuit opening means-comprising a resilient strip, disposed within said casing, supporting means on which saidstrip is .-mounted including a bridge element o'finsulating .material, means :to space said supporting means "fromsaid casing andproviding a sub- ;stantially .rigid .mounting therefor, means anchoring one end of said resilient strip to'said supporting means, the outer end ofsaid resilient strip being'biasecLin a directionperpendic -ular,to,the,axis of said cylindrical casing, away from saidsupporting means, and fusible means engaging the free end portion of said resilient strip (and maintaining the same, against said bias, .in;-a flexurally stressed condition, said fuaSiblQ .means being also supported by said supporting means, the anchored ,end of said resil- .ient,strip being electrically connected to one of said terminal, means, andsaid fusible means he- .ing electrically,rconnected ,to the .otherQone of :13. In apartridgejfuse ,h'avingza -substantially cyclindrical casing "and terminal"means at endsof said casing, circuit opening meanscoim of said terminal means, andsaidfusiblemeans being electrically connected to the other-oneof said terminal means.

,14. A cartridge fuse comprising "a substantially cylindrical casing, terminal means atthe ends of "said casing, a resilient strip disposed within said casing, supporting means on which "said-strip is mounted including abridge element of insulating material and two lagging'elements secured thereto,means tospace said supporting means from said casing and providing *a-sdbstantially rigid mounting therefor, conductor means extending between said terminal means and the end portions of said supporting means, at least one of said conductor means beingfusible under short circuit conditions,means-anchoring one end of said resilient stripto said supporting means and providing electrical connection with one of'said conductor means, means securing" the other one of said conductor means to another portion of said supporting means, an'dfusibl'e means electrically connecting said last-"mentioned conductor means and the'free endportion of said resilientstrip, and maintaining saidresilient strip in 'fiexurally stressed condition.

15. A fuse as claimed in claim 14'in which said conductor means arein the form of strips which overlie the end'portions of said supporting means thereby providing two spaced electrically conducting surfaces, and inwhichsald includes a coplanar portion adapted to .lieagainst both electrically conducting surfaces, and a looped portion between said coplanar portion and the anchored end of said resilient strip, whereby said looped portion is maintained in *flexurally stressed condition ".by

fusible means.

.16. Afuse-as claimedin claim l5r'inwhich .isprovided "a heat absorbing 'membermounted .on said coplanar-portion.

17..,A fuse as claimed in claim 14 having "-a-fuse link .disposed in parallel circuit arrangement with said resilient strip and said 'fusible means.

18. A l'fuse as claimed in claim 15 inwhich said two conductor means and said fuse link constitute a common element.

GUST AJBERTHEL.

References Cited in the ffile'of thispatent UNITED STATES PATENTS Number Name Date 1,792,299 Green Feb. 10,1931 2,004,191 Bussmann .June 11, 193.5 2,113,155 Kiefer Apr. 5, 1938 2,159,423 ,Bussmann Mayn 23, 1939 2,293,953 .Taylor Aug. 25, .1942 2,300,142 Wood .Qct.,2'fl, 1'i42 3,300,620 .Duerkob 'Nov."3,1942 2,532,081 

